Just wondering. We purchased a 1992 Bonneville SSE N/A new for the wife, November 1991. We put 305,000 miles on the car with the original engine and transmission, never anything but maintenance. We stopped driving it because it would not pass emissions. I purchased a 1 owner 2005 Bonneville SE with 58,000 miles on it in 2013(?). The car seamed to be properly maintained. At 112,000 miles the transmission failed.

My take is that GM made a good transmission bad by bean counting it down. The 4t65e is inherently stronger than a 4t60e; but lack of auxiliary cooler, cheap seals without enough lip, poor PCS design/placement, and non-hardened parts where they are needed all contribute to early failures of these units. All of this is correctable with aftermarket parts (upgrades, shift kits, etc.) and it makes for a reliable trans. And of course there are plenty of aftermarket performance parts for the 4t65e.

The 4T60 seems to have less common issues, and with that handles general neglect or lack of service pretty well and for longer than the 65.

My 2003's trans is still going great at nearly 180k miles. Only gives me the very occasional delayed engagement issue. However, I've been pretty good about taking care of it. It's had its fluid changed a few times, two different shift kits, and I think most importantly the cooler.

The 60e has a stronger chain and gears. People used to swap these into the 65s way back when. The vacuum modulator also meant there was one less solenoid to fail. Less 4th clutch hub failures too?

The 65 has a better pump, revs higher without issue, better diff option, and can generally handle more power in stock form. Not to mention GM racing div basically figured out how to make it bullet proof.

It does seem that a 60 behind a S1 will last longer than a 65 behind a S2 but I'm not so sure that's a fair comparo. I feel like most 96 S2 L67 SSEis had premature 60e failures.

I've beat my 03 ssei many times in the 5 or 6 years I've had it. Plenty of burnouts for the grandkids and, a few for grandma but, I cant take her screams any more when I do that. Once in a while the trans stutters when I drop it in gear, other than that it shifts nice at 157K. One thing I forgot is that on the passenger side of the trans output shaft housing, there are 4 threaded holes, one of the bottom holes started leaking trans fluid a few years ago so, I found a bolt and siliconed it in. No idea what happened, something sure did.

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